A card-type electronic apparatus containing a memory device (e.g., an electrically erasable programmable read-only memory (EEPROM) or “flash” memory chip) and other semiconductor components is referred to as a memory card. Typical memory cards include a printed circuit board assembly (PCBA) mounted or molded inside a protective housing or casing. The PCBA typically includes a printed circuit substrate (referred to herein simply as a “substrate”) formed using known printed circuit board fabrication techniques, with the memory device and additional components (e.g., control circuitry, resistors, capacitors, inductors, etc.) formed on an upper surface of the substrate (i.e., inside the casing), and one or more rows of contact pads exposed on a lower surface of the substrate. The contact pads are typically aligned in a width direction of the casing, and serve to electrically connect and transmit electrical signals between the memory chip/control circuitry and a card-hosting device (e.g., a computer circuit board or a digital camera). Examples of such portable memory cards include secure digital (SD) cards, multi media cards (MMC cards), personal computer memory card international association (PCMCIA) cards. An exemplary SD card form factor is 24 mm wide, 32 mm long, and 2.1 mm thick, and is substantially rectangular except for a chamfer formed in one corner, which defines the front end of the card that is inserted into a card-hosting device. The card's contact pads are exposed on its lower surface of each card near the front end. These and other similar card-like structures are collectively referred to herein as “memory module cards” or simply as “memory cards”.
An important aspect of most memory card structures is that they meet size specifications for a given memory card type. In particular, the size of the casing or housing, and more particularly the width and thickness (height) of the casing/housing, must be precisely formed so that the memory card can be received within a corresponding slot (or other docking structure) formed on an associated card-hosting device. For example, using the SD card specifications mentioned above, each SD card must meet the specified 24 mm width and 2.1 mm thickness specifications in order to be usable in devices that support this SD card type. That is, if the width/thickness specifications of a memory card are too small or too large, then the card can either fail to make the necessary contact pad-to-card-hosting device connections, or fail to fit within the corresponding slot of the associated card-hosting device.
Present SD memory card manufacturing is mainly implemented using standard surface-mount-technology (SMT) or chip-on-board (COB) manufacturing techniques, which are well known. The memory, controller and passive devices of each SD card device are typically mounted onto a rigid (e.g., FR or BT material) printed-circuit-board (PCB), which is then mounted inside of a pre-molded plastic housing.
Conventional production methods utilized to manufacture SD card devices present several problems.
First, using SMT methods alone to mount the various electronic components on the rigid PCB has the disadvantage of limiting the number of flash memory devices that can mounted on each SD device due to the thickness and width limitations on the SD card. That is, because the flash memory and controller chips have widths and thicknesses that are defined by the chip packaging dimensions, and because of the restrictions on total thickness of each SD card, only a limited number of packaged flash memory devices can be mounted inside each SD device using SMT methods. The space available for memory devices is further limited by the space needed for the pre-molded plastic housing, which is disposed on both sides of the PCBA. Further, even if room were available inside the housing, it would be too costly to stack “packaged” IC chips, and it would not be practical at present as SD flash card has it own standard shape and form.
Another possible approach to avoiding the vertical space limitations of SMT and pre-molded housings would be to use COB assembly methods to mount IC die onto a rigid PCB, and then using an over-molding process to form the housing. However, this over-molding method has the disadvantage of plastic flash spilling over the connector pins which causes poor electrical contact. Also, it is hard to mold multiple PCBA simultaneously using single molding process, which results in higher manufacturing costs.
What is needed is a method for producing memory cards that maximizes the amount of volume that can be used to house memory and control ICs, and avoids the problems mentioned above that are associated with conventional production methods.